如何使用表达式设置属性值？

Question

考虑以下方法：

public static void SetPropertyValue(object target, string propName, object value) 
{ 
    var propInfo = target.GetType().GetProperty(propName, 
         BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.DeclaredOnly); 

    if (propInfo == null) 
     throw new ArgumentOutOfRangeException("propName", "Property not found on target"); 
    else 
     propInfo.SetValue(target, value, null); 
} 

你会如何去写它的表达能等同，而不需要为目标的额外的参数传递？

为什么不直接设置属性我可以听到你说。例如，假设我们有以下的类有一个公共的getter但私人二传手属性：

public class Customer 
{ 
    public string Title {get; private set;} 
    public string Name {get; set;} 
} 

我想能够调用：

var myCustomerInstance = new Customer(); 
SetPropertyValue<Customer>(cust => myCustomerInstance.Title, "Mr"); 

现在这里是一些示例代码。

public static void SetPropertyValue<T>(Expression<Func<T, Object>> memberLamda , object value) 
{ 
    MemberExpression memberSelectorExpression; 
    var selectorExpression = memberLamda.Body; 
    var castExpression = selectorExpression as UnaryExpression; 

    if (castExpression != null) 
     memberSelectorExpression = castExpression.Operand as MemberExpression; 
    else 
     memberSelectorExpression = memberLamda.Body as MemberExpression; 

    // How do I get the value of myCustomerInstance so that I can invoke SetValue passing it in as a param? Is it possible 

} 

任何指针？

Answer 1

你可以欺骗，让生活更容易扩展方法：

public static class LambdaExtensions 
{ 
    public static void SetPropertyValue<T, TValue>(this T target, Expression<Func<T, TValue>> memberLamda, TValue value) 
    { 
     var memberSelectorExpression = memberLamda.Body as MemberExpression; 
     if (memberSelectorExpression != null) 
     { 
      var property = memberSelectorExpression.Member as PropertyInfo; 
      if (property != null) 
      { 
       property.SetValue(target, value, null); 
      } 
     } 
    } 
} 

然后：

var myCustomerInstance = new Customer(); 
myCustomerInstance.SetPropertyValue(c => c.Title, "Mr"); 

之所以这样，是比较容易的，因为你已经在目标上延方法被调用。此外，lambda表达式是一个简单的成员表达式，没有闭包。在你原来的例子中，目标在封闭中被捕获，并且到底层目标和PropertyInfo可能有点棘手。